The present invention relates to a method of preparing anion exchange resins and the resulting anion exchange resins.
Commercial anion exchange resins are generally prepared by chloromethylation of styrene polymers by means of a mono- or bis-chloromethyl ether, followed by amination. However, as the chloromethyl ethers are carcinogenic and corrosive, they are restricted by very strict rules as to their handling.
Various techniques have been proposed in order to avoid the use of these reagents. These techniques generally consist in (1) treating polymers of alkyl vinyl aromatic compounds with chlorine or bromine, or (2) in polymerizing halogenated alkyl vinyl aromatic compounds, and then aminating the resultant products. However, these techniques are not entirely satisfactory since, in the first case, in addition to the desired halogenation of the alkyl group, the aromatic ring and carbon atoms of the chain are also halogenated, and there is the danger of polyhalogenation of the alkyl group, which is harmful to the preparation of the anion exchanger. In the second case, the halogenated alkyl vinyl aromatic compound to be polymerized is obtained either by direct halogenation, in which case the yield is low due to parasitic reactions, or by a complicated, lengthy technique which may result in losses in yield of product.
The process of the invention makes it possible to prepare anion exchange resins from alkyl vinyl aromatic polymers without the use of chloromethyl ethers and without the aforementioned drawbacks occurring. There is a selective monohalogenation of the alkyl group. There is no halogenation of the aromatic ring, nor of the carbons of the chain and no non-specific interaction.
It is, therefore, an object of the present invention to overcome the drawbacks of the above-described prior art processes.
Another object of the invention is to provide a novel process which provides the above-described advantages.
Further objects will be apparent to those skilled in the art from the present description.